1. Field of the Invention
This invention relates to disc reading apparatuses. More particularly, this invention relates to a disc reading apparatus adapted to read data, through an optical pick-up, out of a recording medium having a spiral track formed thereon.
2. Description of Prior Art
Recording mediums, typically represented by CD-ROMs, have a track on a surface thereof to contain data that has been recorded at a constant linear velocity so as to have constant record density at throughout inner and outer tracks. To read the data out of such a recording medium, the disc is rotatably driven at rotational speeds commensurate with the point being reproduced. That is, the data recorded on the disc is reproduced by varying the rotational speed of the disc matched to the reproducing point. However, there has been a problem that data cannot be read out until the disc rotational speed reaches a speed matched to a point to be reproduced. To cope with this, there is a conventional method in general use for reading out data, wherein the area that can record data conforming to ISO9660 is divided into a plurality of zones beforehand so that each zone has a rotational speed set such that the data can be read at a maximum fast speed.
However, if the data to be read resides over a plurality of zones, the disc rotational speed has to be varied during data reading. Consequently, when reading the data in the next zone, there is a necessity of waiting for reaching the disc rotational speed to a speed for the zone. Furthermore, the disc rotational speed is determined for each zone based on the rotational or reading speed for reading at an outer circumference of a data-recordable area. Therefore, where the amount of data recorded on the disc is comparatively small, i.e. where the radius of the outer circumference of the data-recorded area is small in comparison with the outer radius of the data-recordable area, there has been a problem that it is impossible to read data at speed expected from signal processing capability or disc motor power performances.